This invention relates in general to earth boring bits, and in particular to surfaces in a bit for absorbing outward thrust of the cutter on the bearing pin.
Conventional earth boring bits have a body with three depending bearing pins, each of which receives a rotatable conical cutter. Journal or roller bearings between the cutter and bearing pin absorb large forces imposed on the bit during drilling. Normal downward drilling also causes the cutter to exert an outward force on the bearing pin, tending to push the cutter farther onto the bearing pin. This outward thrust is handled by one or more thrust surfaces located between the cutter and bearing pin in a plane perpendicular to the axis of the bearing pin. Usually these thrust surfaces have inlays of hard metal to reduce the wear on the thrust surfaces.
One type of bit is particularly used in the mining industry for drilling blast holes of relatively short depth. Compressed air is pumped through the drill bit for cooling the bit and blowing cuttings to the surface. Some of the air is diverted through the bearing areas for cooling the bearings. One of the thrust surfaces comprises opposed shoulders on the bearing pin and in the cutter. If these thrust shoulders wear sufficiently, the backface of the cutter will contact the last machined surface of the bit leg, resulting in locking and destruction of the bit. Improving the wear resistance of the shoulders is a long standing problem.